Automatic trip circuit breaker



Dec. 20, 1949 w. DYER AUTOMATIC TRIP CIRCUIT BREAKER 2 Sheets-Sheet 1Filed Jari. `18, 194e wm R.. ||l Q. @L n w1 v w @n n \Q\ Q nm. In QW mw2.. frz mh. l MIN.

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ATTORNEY 2 Sheets-Sheet 2 Dec. 20, 1949 w, DYER AUTOMATIC TRIP CIRCUITBREAKER Filed Jan. 18, 1946 Patented Dec. 20, 1949 AUTOMATIC TRIPCIRCUIT BREAKER Lloyd W. Dyer, Pittsburgh, Pa., assgnor to WestinghouseElectric Corporation, East Pittsburgh, Pa., a corporation ofPennsylvania 4 Application January 18, 1946, Serial No. 642,037

(Cl. G-88) 11 Claims.

This invention relates to circuit breakers, and more particularly tocircuit breakers of the type which are tripped instantaneously onoverload currents of predetermined magnitude and after a time delay onlesser overloads.

One object of the invention is to provide a circuit breaker with animproved sealed-in trip device having adjusting means for varying themagnetic tripping point of the breaker and calibrating means fordetermining the range of adjustment.

Another object of the invention is to provide a circuit breaker with animproved trip device disposed in a sealed casing and having adjustingmeans accessible externally of said casing for varying the magnetictripping point of the breaker, and Calibrating means settable beforesaid casing is sealed to determine the range of adjustment .of saidadjusting means.

Another object of the invention is to provide a circuit breaker with animproved trip device comprising an electromagnet and an armatureoperable to trip the breaker, a releasable trip member operable to tripthe breaker, a single spring for biasing the armature against operationand for operating said releasable trip member, adjustable means forvarying the magnetic tripping point of the breaker, and means forcalibrating the range of adjustment, all of said parts being enclosed ina sealed casing and said adjustable means being accessible through saidcasing.

Another object of the invention is to provide a circuit breaker with animproved trip device according to the preceding paragraphs, wherein theentire trip device is removable and replaceable as a unit withoutaffecting the tripping point of the device.

The novel features that are considered characteristic of the inventionare set forth in particular in the appended claims. The inventionitself, however, both as to structure and operation, together withadditional objects and advantages thereof, will be best understood fromthe following detail description with the embodiment thereof when readin conjunction with the accompanying drawings.

In said drawings:

Fig. 1 is a front elevational view of a circuit breaker embodying theprinciples of the invention, the cover being partly broken away to moreclearly show some of the parts.

Fig. 2 is a front elevational view of a part of the circuit breakershown in Fig. 1 with a part of the breaker cover and a part of the tripdevice cover broken away to more clearly show some of the parts of thetrip device.

Fig. 3 is a detail view of the trip device adjusting cam; and

Fig. 4 is a vertical sectional view of the circuit breaker takensubstantially along line IV-IV of Fig. l, the breaker being shown inclosed circuit position.

Referring to Figures 1 and 4 of the drawings, the circuit breakerincludes a base I I of moulded insulating material on which the severalelements of the breaker mechanism are mounted. A cover I2 also ofmoulded insulating material is removably secured to the base andcooperates there- With to form an enclosing housing for the breakermechanism.

The circuit breaker is of the multipole type. each pole comprising apair of terminals I3 and I5, one disposed at each end of the breaker, astationary contact I'I, an arc extinguisher I9, and a movable contact2I. A common operating mechanism indicated generally at 22 is providedfor simultaneously actuating the three movable contacts to open or toclosed position, and a trip device indicated generally at 23 serves toeect automatic opening of the three sets of contacts in response topredetermined overload conditions in the circuit through any pole of thebreaker.

Each of the movable contacts 2| is mounted on a contact arm 25 pivotallysupported intermediate its ends on the free end of a pair of switch arms2l by means of a pivot pin 26. The arms 21 for all of the poles aremounted on a rectangular tie bar 29 of insulating material, and eachpair of the arms 2'I is joined by a rectangular sleeve 3I surroundingthe tie bar and secured Ilthereto so that said tie bar and all of theswitch arms 21 rotate as a unit, the tie bar being pivotally supportedin the side walls of the breaker. The tie bar 29 extends transverselyacross the three poles of the breaker.

A exible shunt conductor 30 connects the contact arm 25 with an angularterminal 32 secured by a screw 33 to one end of a conductor 35. Thescrew 33 also serves to secure the conductor 35 to the base II. Theother end of the conductor 35 is formed into an energizing winding 36 ofa trip magnet (to be described later) and is connected by a flexibleconductor 31 to a point near the free end of a thermally responsivebimetal element 39. The other end of the bimetal 39 is rigidly securedto the incr end of a conductor 4I, the terminal I5 being secured to theouter end of said conductor. Each of the stationary contacts I'I ismounted on the inner end of a conductor 43 having its outer endconnected to the terminal |3. y

The electrical circuit for each of the poles 1s essentially the same andextends from the terminal |3 through the conductor 43, stationarycontact |1, the movable contact 2|, the contact arm 25, the flexibleshunt conductor 30, the terminal 32, the conductor 35, winding 36, theiiexible shunt conductor 31, the bimetal clement 39 and the conductor 4|to the terminal |5 Each of the three poles of the breaker is-containedin a separate compartment formed by barriers 42 (Figs. 1, 2, and 4)moulded integral with the base and extending to the trip device. Thesebarriers 42 are in alignment with similar barriers 45, (Fig. 4) mouldedintegral with the cover |2 so that when the cover is in place thebarriers 42 and 45 serve to insulate each compartment from the adjacentcompartments and prevent flashovers.

The tie bar 29, which extends across all three poles of the breaker, isprovided with annular iianges 48 disposed in recesses in the sides ofthe barriers 42 to prevent flashover through the openings in thebarriers 42 provided to accommodate the tie bar.

The operating mechanism for the breaker 11- lustrated generally at 22(Fig. 4) is disposed in the compartment housing the center pole and issupported on a pair of frames 44 secured to the center part of the baseil. The operating mechanism includes a forked operating lever 41, atoggle comprising links 49 and 5|, a pair of overcenter springs 53, anda releasable cradle 55 controlled by the trip device 23. The cradle 55is pivotally supported on the frame 44 by a pivot pin 56. The inner endsof the forked operating lever 41 are rounded and are pivotally seated inrecesses in the frame 44 as indicated at 51. An insulating shield 59 forcovering an opening 6| in the cover I2 is mounted on the outer end ofthe operating lever 41 and a Inanual operating handle 63 integral withsaid shield projects through the opening 6| to permit manual operationof the breaker mechanism.

The ltoggle links 49 and 5| are pivotally con- Ynected together by aknee pin 65. The link is pivotally connected by a pivot pin 61 to thepair of switch arms 21 for the center pole, and

the end of the link 49 is bifurcated and pivotally Overcenter springs11, operatively associated` with the contact arms 25, surround contactarm operating members 19 and are compressed between angular brackets BIsecured to the pivoted ends of the arms 21 and shoulders 83 on themembers 19. The springs 11 hold the ends of the members 19 in engagementwith recesses in the inner ends of the contact arms 25. The members 19and the contact arms form toggles for operating the contact arms 25.

As previously mentioned, the trip device 23 includes a bimetal element39 for each of the poles of the breaker, said bimetal elements be ingconnected in series in the circuit of their respective poles. The tripdevice also includes a series overload magnet 86 for each pole, anda'trip bar 81 common to all of the poles. The trip bar 81 is of onepiece moulded insulating material and is pivotally supported by means ofpins 89 moulded in axial alignment in the ends of the trip bar and whichrotatably support said bar in bearings 9| (Fig. 1) in the side walls ofthe circuit breaker housing.

The trip bar 81 extends across the three poles of the breaker throughopenings provided therefor in the barriers 42 and 45. The trip bar 81 isprovided with a latch member secured to projections 92 moulded integralwith the trip bar 81 and normally engages the latch end of the cradle55, thereby restraining the cradle in operative position. In order tomore completely insulate the compartments, the trip bar 81 is providedwith a plurality of flanges 88 moulded integral with said trip bar anddisposed one on each side of each of the barriers 42 and 45. Theseflanges are positioned close to the bar.- riers and effectively preventflashover through the opening provided in the barriers for the trip bar81.

The trip device 23 is of the renewable type and is enclosed in a sealedhousing of moulded insulating material comprising a base and a cover 91which are suitably secured together and sealed after the trip mechanismis assembled therein and adjusted. The housing 95-91 is divided intothree compartments for separately enclosing the individual trip devicefor each of the three poles of the breaker. The compartments are formedby partition walls 99 moulded integral with the base 95 and matchingpartition walls ||l| moulded integral with the cover 91.

The trip devices for the terminal poles are the same for which reasononly the one illustrated, which is for the center pole, will bedescribed. The trip device comprises a trip lever 93 pivotally supportedon a pin |03 mounted in the partition walls 99 of the base 91 of thetrip device housing. 'I'he trip lever 93 is provided with a latch end|05 which is biased by means of a pair of springs |01 (Fig. 2) intolatching engagement with a latch member |09 mounted on the free end ofthe bmetal element 39. The springs |01 are disposed one on each side ofthe trip lever 93 and are compressed between projections on the tripmember 93 and a bracket 3 mounted on an armature I5 which forms a partof the eiectromagnet 86.

The armature ||5 is pivoted on a pin H1 supported in spaced projectionson the upper end of an L-shaped magnet yoke ||9. The magnet yoke ||9 issecured by means of a screw |2| to the base 95 of the trip devicehousing and is provided with a core member |23 which extends into thewinding 36 of the tripping electromagnet 86.

An adjustable stop screw |25 (Fig. 4) is provided in a formed portion|21 of the armature to limit the clockwise movement of the armature ||5.This stop is adjusted before the assembled trip unit is installed in thebreaker. y

Means are provided for varying within a predetermined range the minimumoverload current required to trip the breaker without removing eitherthe cover of the breaker or the sealed trip device cover. This meanscomprises an eccentric cam' member |29 (Figs. 3 and 4) provided withspaced notches 3| in its cam surface. The cam |29 is mounted on a pin|33 and is supported by a shoulder on the pin resting upon a U-shapedbracket |35, the two legs of which are secured by means of screws |31(only one being shown) to the partition walls 99 of the base 95. Thereduced lower end of the pin |33 extends through an opening in thebracket |35 to provide a pivot for the cam |29. One end of an angularadjusting lever |39 pivoted on the pin |03 is provided with a small,conical projection |4| (Fig. 3) which is adapted to engage the notches|3| in the cam |29 to retain the cam in its adjusted position. The otherend of the lever |39 bears against a projection |43 on the bracket ||3which supports one end of the spring |01. A spring |44 coiled about thepin |03 having one end hooked over the lever |39 and the other endhooked over the trip lever 93 biases the adjusting lever |39 intoengagement with the adjusting cam |29.

The spring |01 is, therefore, common to bot-h the trip lever 93 and thearmature ||5 serving to bias the trip lever 93 against the latch |09,and, at the same time, biases the armature |5 against the adjustinglever |39. It will be obvious that rotating the cam |29 will operate thelever |39 and vary the air gap l 5|23 thereby varying the minimumcurrent value required to trip the breaker.

The cam |29 is rotated by means of an adjusting screw |45 which has anopening therein for engaging a serrate hub |41 integral with the cam|29. The adjusting screw |45 extends through an opening in the cover 91of the trip device and partially through a. corresponding opening in thecover |2 of the circuit breaker, and is accessible for adjusting thetripping point of the trip magnet 86 without removal of either thebreaker cover or the trip device cover. An annular shoulder |49 on thescrew |45 prevents removal of the screw and changing of the relativeposition of the screw |45 and cam |29 without removal of both of thecovers.

Before the cover 91 of the trip device is assembled and sealed in place`the adjusting screw |45 is removed and the cam |29 is rotated to adjustthe armature for the desired tripping current values, that is, theminimum current value at which it is desired that the tripping magnetwill function to instantaneously trip the breaker. The adjusting screw|45 is then replaced on the hub |41 of the cam |29 in the properlocation corresponding to the low calibration mark on the cover 91. Thecover 91 is then assembled and sealed on the base 95 after which themain break er cover I2 is installed.

It will be noted that neither the armature ||5 nor the trip member 93have any mechanical connection with the trip bar 81. Thus the trip unitmay be removed and another unit installed in the breaker withoutdisturbing the position of the trip bar and without affecting thetripping point of the breaker as would be the case if there was acritical latch point between the trip device and r the releasableoperating mechanism.

When the bimetal element 39 for any one of the poles is heated apredetermined amount in response to an overload current, it flexes in adirection to move the free end thereof toward the left (Fig. 4) andafter a time delay unlatches the trip lever 93, whereupon the spring |01rocks the trip lever sharply clockwise. During this movement, the end ofthe lever 93 which is disposed above a projection |5| moulded integralwith the trip bar, strikes said projection and rocks the trip bar 81counterclockwise causing the latch 90 to release the cradle 55. Thispermits the overcenter springs 53 to rotate the cradle clockwise aboutits pivot 55 to effect opening of the contacts. At the start of theoperation of the cradle 55 a projection 68 thereon engages a stud 66 onof the toggle link 49 to move to the right of the line of action of theovercenter springs 53 which Athen act to complete the collapse of thetoggle. This rocks the arms 21 counterclockwise carrying the contactarms 25 counterclockwise therewith to open the circuit of the breaker.This operation of the mechanism also causes the handle 63 to be moved toan indicating position intermediate the open and closed positions.

In the closed circuit position (Fig. 4) the line of action of theovercenter spring 11 is above the pivot 26 of the contact arm 25 andbiases the contact arm in a clockwise direction about its pivotproviding pressure for the contacts. `When the arms 21 are rotatedcounterclockwise, as above described, a vtail |53 on the toggle member19 strikes a projection |55 on the base causing the toggle 19-25 to moveovercenter. This rocks the contact arm 25 counterclockwise about itspivot 26l which opens the contacts a greater distance than would bepossible if the movable contacts were mounted directly on the arms 21.

The trip device is also operated electromagnetically by means of thepreviously described electromagnet 86 (Fig. 4) to instantaneously tripthe breaker upon the occurrence of a heavy overload, for instance, 1000%or more of rated current, or on short circuits in the circuit of anypole of the breaker.

Upon the occurrence of such an overload current, or a short circuit, thearmature ||5 is attracted with sufficient force to engage an arm |51thereof with a projection |59 on the trip bar 81 and operate the tripbar to release the cradle 55 and eiect opening of the contacts in theman ner previously described.

Following each automatic operation of the breaker due to operation ofthe trip device 23 in response to an overload current, it is necessaryto reset the mechanism to operative condition before the contacts can bereclosed. This is effected by rotating the manual lever 41 from itstripped position to its extreme counterclockwise or open position. Thismovement of the lever 41 is transmitted to the cradle 55 by a hookedprojection |63 engaging a portion of the cradle. As the cradle 55 isrotated in a counterclockwise direction, the latch end thereof passesthe latch member 90 and engages a projection |6| molded integral withthe trip bar 81, rocking the trip bar clockwise slightly past its normalposition to relatch the cradle 55. During the clockwise resettingmovement of the trip bar 81, the projections |5| thereon engage the endsof the trip levers 93 and rock said levers counterclockwise to relatchthem with the latches |09 on the bimetal elements 39.

. After the cradle 55 has been relatched, the contacts can be closedmanually by moving the lever 41 clockwise to its closed circuitposition. During this movement, the line of action of the overcentersprings 53 crosses to the right of the pivot 69 of the toggle link 49causing the toggle 49-5I to move overcenter and rock the arms 21 quicklyclockwise to close the contacts. As the switch arms 21 approach theclosed position, the arm 25 strikes a projection |65 on the base at apoint to the left of the pivot 26 (Fig. 4) causing clock-wise rotationof the contact arm 25 about its pivot 26 moving the spring 11 overcenterabove the pivot 26. This causes the contacts to close with a snap actionand applies' pressure to the closed contacts after they are closed.

The contacts are opened manually by moving the lever 41 in acounterclockwise direction about its pivot to the open position. Thismovement carries the line of action of the springs 53 to the left of thepivot 69 of the toggle link 49 and the force exerted by said springs nowbiases the toggle 49-5! away from its overcenter position. Before thelever 41 reaches its extreme counterclockwise or open position, thisforce becomes sufficient to cause the toggle to quickly collapse, andsince the toggle link I is pivotally connected to the switch arms 21 forthe central pole, these arms are rotated counterclockwise causingopening of the contacts for all of the poles. The contacts are closedmanually in the manner previously described.

The circuit breaker is trip free, i. e., operative automatically inresponse to predetermined abnormal circuit conditions in any one of thepoles thereof irrespective of the position of the operating lever 41.

The arc extinguishers I9, there being one provided for each pole of thebreaker, are of the spaced plate type and comprise, generally, a stackof slotted plates of magnetic material positioned adjacent the paths ofmovement of the movable contacts 2|. The presence of these plates causesthe arc resulting from the rupture of the circuit to be drawn in thedirection toward the ends of the slots where the arc is broken up into aplurality of short arcs, and these short arcs are quickly cooled andextinguished.

The structural details of the circuit breaker operating mechanism andthe operation thereof are fully described in Patent No. 2,318,298,issued May 4, 1943, to H. D. Dorfman and Gerald J.

greese and assigned to the assignee of this inven- Having described thepreferred embodiment of the invention in accordance with the patentstatutes, it is to be understood that various changes and modificationsmay be made in the structural details disclosed without departing fromsome of the essential features of this invention. f

I claim as my invention:

1. In a circuit breaker comprising relatively movable contacts andactuating means for opening said contacts, a trip bar releasablyrestraining said actuating mechanism, electromagnetic means responsiveto overload currents above a predetermined value, an armature operableby said electromagnetic means to engage and operate said trip bar tocause release of said actuating means, a releasable trip member operableto engage and operate said trip bar independently of said armature tocause release of said actuating means, spring means compressed betweensaid releasable trip member and said armature for actuating said tripmember upon release thereof and for biasing said armature to unattractedposition, and a bimetal element operable when heated a predeterminedamount to release said trip member.

2. In a circuitV breaker comprising relatively movable contacts andactuating means therefor, a trip bar operable to cause automaticoperation of said actuating means, a trip device responsive to overloadcurrents for operating said trip bar, said trip device including asealed casing, an electromagnet including an armature provided with aportion extending outside of said casing and operable to engage andoperate said trip bar, a releasable trip member extending outside ofsaid casing, spring means common to said arma- 8 ture and said tripmember for biasing said armature to unattracted position and foractuating said trip member independently of said armature to engage andoperate said trip bar, means for calibrating said trip device beforesaid casing is sealed, and an adjusting means operable with-A,

out removing said casing to adjust the tripping point of said breakerwithin a predetermined range.

3. In a circuit breaker comprising relatively movable contacts andoperating means therefor, a trip bar releasably restraining saidoperating means and operable to cause automatic opening operation ofsaid operating means, trip means operatively associated with said tripbar but having no mechanical connection therewith for engaging andmoving said trip bar to effect release of said operating means upon theoccurrence of a predetermined overload current, means for calibratingsaid trip means, a sealed cover enclosing said trip means and saidCalibrating means, means accessible without removing said sealed coverfor adjusting the tripping point of said breaker within a predeterminedrange, and said trip means and said Calibrating means being removableand replaceable as a unit without affecting the tripping point of thebreaker and without disengaging any connection with said trip bar.

4. In a circuit breaker comprising relatively movable contacts andoperating means therefor, a trip member releasably restraining saidoperating means and operable to release said operating means to causeautomatic operation of said operating means, a removable trip unitcomprising a sealed casing, trip means mounted in said casing and havinga portion extending outside of said casing separably engageable withsaid trip member but having no connection thereto, calibrating meansdisposed in said sealed casing and adjustable before said casing issealed to calibrate said trip means, and adjusting means accessiblethrough said casing for varying the tripping point of said breaker, saidtrip unit being removable and replaceable as a unit without disengagingany connection with said trip member and Without disturbing the trippingpoint of said breaker.

5. In a circuit breaker comprising relatively movable contacts andoperating means therefor, a removable trip unit comprising a sealedcasing, a trip member disposed outside of said casing operable to causeautomatic opening movement of said operating means, trip means disposedin said casing and having a part extending externally of said casing forengaging and operating said trip member, said part having no mechanicalconnection with said trip member to permit removal of said trip unitwithout disengaging any connection with said trip means, adjusting meansaccessible externally of said sealed casing for varying the trippingpoint of said breaker within a predetermined range, Calibrating meanssettable said trip bar, a releasable trip member extending; externallyof said casing for engaging and operating said trip bar, spring meanscommon to said armature and said releasable trip member biasing saidarmature to unattracted position and for operating said releasable tripmember, means accessible externally of said casing for adjusting saidarmature to vary the tripping point of the breaker within apredetermined range, ca1ibrat ing means settablebefore said casing issealed to determine the range of adjustment of said adjusting means andsaid armature and said releasable trip member having no connection tosaid trip bar to permit removal of said trip unit without disengagingany connection with said trip bar and without disturbing the adjustmentand calibration of said trip means.

7. In a multipole circuit breaker comprising a plurality of sets ofrelatively movable contacts and operating means therefor, a trip unitcomprising a sealed casing having partition walls therein formingseparate compartments, a trip bar disposed outside of said casing andcommon to all of the poles of said breaker for releasably restrainingsaid operating means, trip means disposed in each of compartmentsassociated with said trip bar outside of said casing for engaging andoperating said trip bar upon the occurrence of an overload current inthe associated pole, said trip means being separable from said trip barwithout disengaging any connection with said trip bar to facilitateremoval and replacement of said trip unit, separate adjusting means foreach of said trip means accessible through said casing for varying thetripping point of the associated trip means within a predeterminedrange, and Calibrating means associated with each adjusting means, eachof said Calibrating means being settable before said casing is sealed todetermine the range of adjustment of the associated adjusting means.

8. In a multipole circuit breaker comprising a plurality of sets ofrelatively movable contacts and operating means therefor, a trip unitcomprising a sealed casing having partition walls therein formingseparate compartments, a trip bar disposed externally of said casing andcommon to all of the poles of said breaker for releasably restrainingsaid operating means, trip means vdisposed in each of compartments andhaving portions extending outside of said casing associated with saidtrip bar for engaging and operating said trip bar upon the occurrence ofan overload current in the associated pole, said portion of said tripmeans having no mechanical connection with said trip bar, separateadjusting means for each of said trip means accessible through saidcasing for varying the tripping point of the associated trip meanswithin a predetermined range, and Calibrating means associated with eachadjusting means, each of said calibrating means being settable beforesaid casing is sealed to determine the range of adjustment of theassociated adjusting means, and said trip unit being removable andreplaceable without disengaging any connection with said trip bar andwithout aiTecting the tripping point of any of said trip means.

9. In a multiple circuit breaker comprising a plurality of sets ofrelatively movable contacts and operating means therefor, a trip unitcomprising a sealed casing having partition walls therein formingseparate compartments, a trip bar common to all of the poles of saidbreaker disposed externally of said sealed casing, trip `overloadcurrent in the associated pole, said trip means having no mechanicalconnection with said trip bar, separate adjusting means 'for each ofsaid trip means accessible through said casing for varying the trippingpoint of the associated trip means within a predetermined range,callbrating means associated with each adjusting means, each of saidCalibrating means being settable before said casing is sealed todetermine the range of adjustment of the associated adjustingT means,the range of adjustment of each of said adiusting means being xed whensaid casing is sealed, and said sealed casing together with said tripmeans and said adjusting means being removable as a unit withoutdisengaging any connection with said trip bar and without disturbing theadjustment and calibration of said trip means.

10. In a multipole circuit breaker comprising a plurality of sets ofseparable contacts and operating means therefor, a trip unit comprisinga Sealed casing having partition walls therein forming separatecompartments, a trip bar disposed outside of said sealed casing andcommon to at least two poles of the breaker and operable to causeautomatic opening operation of said operating means, an electromagnetictrip device including an armature disposed in each compart-' ment andhaving a portion extending outside said casing for engaging andoperating said trip bar, a releasable trip member disposed in eachcompartment and having a portion extending outside said casing forengaging and operating said .trip bar independently of said armature,spring means in each compartment compressed between the associatedarmature and said trip member for biasing the associated armatureagainst attraction and for operating the associated releasable tripmember, means disposed in each compartment and accessible externally ofsaid casing for individually adjusting said armatures to vary thetripping point of the associated trip device within a predeterminedrange, and separate calibrating means for each trip device settablebefore the casing is sealed to separately determine the range ofadjustment for each of said adjusting means;

11. In a multipole circuit breaker comprising a plurality of sets ofseparable contactsiand operating means therefor, a trip unit comprisinga sealed casing having partition walls therein forming separatecompartments, a trip bar disposed outside of said sealed casing andcommon to at least two poles of the breaker and operable to causeautomatic opening operation of said operating means, an electromagnetictrip device including an armature disposed in each compartment andhaving a portion extending outside of said casing for engaging andoperating said trip bar, a releasable trip member disposed in Ieachcompartment and having a portion extending outside of said casing forengaging and operating said trip bar independently of said armature,spring means in each compartment compressed between the associatedarmature and trip member for biasing the associated armature againstattraction and for operating the associated releasable trip member,means disposed in each compartment and accessible externally of Saidcasing for individually adjusting said armatures to vary the trippingpoint of the associated trip device within a predetermined range, andseparate calibrating means for each trip device settable before thecasing is sealed to separately determine the range of adjustment .foreach of said adjusting means, said trip unit being removabieandinterchangeable without affecting the tripping point of any of said tripdevices.

' v LLQYD w. DYER.

REFERENCES CITED l The following references are of record in the me ofthis patent:

Number 12 i UNITED STATES PATENTS Name Date Wheeler Dec. 24, 1901 StolzJune 16, 1936 Graves, Jr. Mar. 23, 1937 Jennings Dec. 13, 1938 TusingOct. 10, 1939 Sachs Dec. 5, 1939 Dorfman Dec. 2, 1941 .Baxter et a1.July 6, 1943 FOREIGN PATENTS Country Date Number Germany Nov. 21. 1939

